1. Field of the Invention
This invention relates to a failure diagnosis device of an exhaust gas recirculation (hereinafter, EGR) control device wherein when a failure diagnosis is performed on the EGR control device which recirculates a portion of the exhaust gas of an internal combustion engine back to an intake pipe of the internal combustion engine, the time to close an EGR pipe is made as short as possible, thereby alleviating mental shock to a driver, and preventing deterioration of the exhaust gas.
2. Discussion of Background
A conventional failure diagnosis device for an EGR, control device controls the opening and closing of the EGR pipe, memorizes running conditions of the engine when the device performs opening and closing operations, respectively, and determines the failure of the EGR pipe by the difference between the two memorized values, as disclosed in Japanese Unexamined Patent Publication No. 51746/1987.
With the conventional failure diagnosis device of an EGR control device is composed as above, the opening and closing of the EGR pipe for the failure diagnosis are performed when the engine is in a steady state. Furthermore, since the conventional device compares predetermined running conditions (for instance, intake pipe pressures) when the opening of the EGR pipe is operated, with those when the closing of the EGR pipe is operated it is necessary to continue the closing operation of the EGR pipe until a predetermined running condition in the closing operation becomes stabilized. Therefore it is necessary to continue the steady state of the engine until the running condition is stabilized.
Furthermore, the above closing operation causes mental shock to a driver, and deteriorates exhaust gas emission more than before the operation when the EGR control devices are normally operated.